Coherence between oxygen saturation and heart rate obtained from pulse oximetric recordings in obstructive sleep apnoea.

In obstructive sleep apnoea (OSA) cyclical changes in oxygen saturation and heart rate in the period range of 30-120 s are observed. In these patients, we prospectively analyse the coherence of nocturnal SaO(2) and heart rate signals. A sample of 201 clinically suspected of having OSA were studied using nocturnal pulse oximetric and complete polysomnography. Coherence function versus period curves were categorized into three patterns: a positive pattern showing a predominant positive peak value of coherence in the period range of 30-120 s; a negative pattern if the predominant coherence was negative in the same range; and an undetermined pattern if no predominance was detected. One hundred and thirteen patients present a positive coherence pattern; 74.3% of these have OSA. A negative coherence pattern was observed for 28 patients; 85.7% of these have OSA. The remaining 60 patients present an undetermined pattern. Patients with OSA presented significantly higher maximal positive coherence and maximal negative coherence than those without OSA. We conclude that OSA patients present dynamic coordination and interdependence between SaO(2) and heart rate in specific frequencies.